1. Field of the Invention
This invention relates generally to shield cases for radio-frequency appliances and, more particularly, to a shield case for a radio-frequency appliance formed in a state of development by blanking a metal sheet such as of iron, stainless steel, aluminum, copper or phosphor bronze to be assembled upon being mounted onto a circuit board.
2. Description of the Prior Art
For the radio-frequency appliances, there is a proposal of doubly providing the shield plates in order to exclude radio-frequency interference.
FIGS. 1 and 2 show a first prior art of a shield case for a radio-frequency appliance of this kind. FIG. 1 shows an assembled state while FIG. 2 a development state. The first prior-art shield case includes two side plates 2 and 3 formed by blanking a metal sheet and two shield plates 4 and 5 formed connected to the side plates 2 and 3 through connecting portions and arranged close to each other due to assembling. Protuberances 4a and 5a are formed in respective opposite end edges of the two shield plates 4 and 5 in a development state, so that they can be inserted in a circuit board (not shown) and connected to a reference potential. Also, a recess 4b can be formed in an end edge of the shied plate 4 opposite to the protuberance 4a so that it can be engaged with a shield plate 6 due to assembling.
In assembling the first prior art, the shield plates 4 and 5 are twisted such that the surfaces of the shield plates 4 and 5 shown in FIG. 2 are positioned outward. The protuberances 4a and 5a are inserted in and soldered to the insertion holes of the circuit board. Thereafter, a protuberance 6a of the shield plate 6 is inserted in a circuit-board hole in the similar manner and a protuberance 6b is engaged with the recess 4b of the shield plate 4.
In the case of a second prior-art shield case 1 shown in FIG. 3 and FIG. 4, a metal sheet is blanked in a manner similar to the first prior art, to form two side plates 2 and 3 as well as two shield plates 4 and 5 connected between the side plates 2 and 3 through connecting portions. Protuberances 4a and 5a are formed in end edges of the two shield plates 4 and 5 on the same side in a development state. In this case, a recess 5b is formed in an end edge of the shield plate 5 in order to allow the protuberance 4a of the shield plate 4 to escape.
In assembling the second prior art, the shield plates 4 and 5 are twisted such that one of the surfaces of the shield plates 4 and 5 shown in FIG. 4 is on an inner side and the other outward. The protuberance 4a and 5a are inserted in and soldered to the insertion holes of the circuit board.
In the first prior art, the shield plate 6 is formed as a separate member thus increasing the number of parts. However, in the first prior art, the shield plate 6 can be formed in one body with the shield plate 4 if increasing the distance between the shield plate 4 and the shield plate 5. In this case, however, the shield case will increase in size. Therefore, the shield plate 6 must be made as a separate member in the case there exists a restriction in space or shape.
In the second prior art, where the spacing between the shield plate 4 and the shield plate 5 has to be decreased due to the limitation of circuit arrangement or the like, the recess 5b of the shield plate 5 must be made greater as the two shield plates 4 and 5 are arranged closer to each other, thus resulting in deterioration in shield effects.
Therefore, it is a primary object of this invention to provide a novel shield case for a radio-frequency appliance.
Another object of the invention is to provide a shield case for a radio-frequency appliance capable of comparatively freely coping with circuit arrangement and securing shield effects while having side plates and shield plates formed by blanking one metal sheet.
A shield case for a radio-frequency appliance according to the present invention comprises: first and second side plates formed by blanking a metal sheet; first and second shield plates formed with spacing between the first side plate and the second side plate; a first connecting portion connecting the first shield plate to both the first side plate and the second side plate; a second connecting portion connecting the second shield plate to both the first side plate and the side plate; a first bending allowance formed between the first connecting portion and the second connecting portion of the first side plate; a second bending allowance. formed between the first connecting portion and the second connecting portion of the second side plate, wherein the first bending allowance and the second bending allowance during assembling are bent inward between the first shield plate and the second shield plate.
Where a projection for setting a reference potential is provided in the shield plate, a protuberance is formed protruding toward the second shield plate from a first end edge of the first shield plate on a side close to the second shield plate in a development state, wherein the first bending allowance and the second bending allowance are set each to have a length greater than a length of the protuberance.
Where integrating a third shield plate, a third shield plate is formed in a second end edge of the first shield plate on a side opposite to the first end edge through a third connecting portion.
If there is reduction in shield effect when bending inward the bending allowances, the bent portions at outer side are shielded by the engaging portions. Specifically, the first bending allowance is formed in a widthwise part of the first side plate and the second bending allowance is formed in a widthwise part of the second side plate, further comprising a first engaging portion to be engaged with another widthwise portion of the first side plate by sandwiching the first bending allowance; and a second engage portion to be engaged with another widthwise portion of the second side plate by sandwiching the second bending allowance, wherein when the first bending allowance and the second bending allowance are bent inward, the first engaging portion is engaged together and the second engaging portion is engaged together.
When assembling a shield plate having, in a development state, a first bending allowance formed between a first connecting portion and a second connecting portion of the first side plate and a second bending allowance formed between a first connecting portion and a second connecting portion of the second side plate, the first and second side plates as well as the first and second shield plates are twisted by 90 degrees to a perpendicular position to a circuit board. In this case, because the first and second bending allowances are bent inward between the first and second shield plates, the spacing between the first and second shield plates, even if great in the development state, can be decreased. For example, where forming protuberances in the side end edges of the first and second shield plates in the development state, the distance between the first shield plate and the second shield plate increases. In such a case, however, it is satisfactory to set the first and second bending allowances with length greater than a length of the protuberance in the development state and these bending allowances are bent inward during assembling.
According to the present invention, one metal sheet is blanked so that a sheet left is bent to form various portions into one body, thus reducing the number of parts and simplifying assembling operation. Furthermore, as compared to combination with separate parts, positional accuracy is improved and electric characteristic is stabilized, resulting in improved quality. Meanwhile, it is possible to reduce cost, i.e. the die cost required for separate parts. Furthermore, the provision of bending allowances allows for setting, in a development state, a spacing between the first and second shield plates freely, thus simplifying design.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.